How a JEE6 enterprise application that offers REST web services should be organized?

design-patterns, jakarta-ee, java, jax-rs, rest

Solution

Below is an example of a JAX-RS service implemented as a session bean using JPA for persistence and JAXB for messaging might look like. (note an `EntityManager` is injected onto the session bean, why do you want to avoid this kind of behaviour?):

package org.example;

import java.util.List;

import javax.ejb.*;
import javax.persistence.*;
import javax.ws.rs.*;
import javax.ws.rs.core.MediaType;

@Stateless
@LocalBean
@Path("/customers")
public class CustomerService {

    @PersistenceContext(unitName="CustomerService",
                        type=PersistenceContextType.TRANSACTION)
    EntityManager entityManager;

    @POST
    @Consumes(MediaType.APPLICATION_XML)
    public void create(Customer customer) {
        entityManager.persist(customer);
    }

    @GET
    @Produces(MediaType.APPLICATION_XML)
    @Path("{id}")
    public Customer read(@PathParam("id") long id) {
        return entityManager.find(Customer.class, id);
    }

    @PUT
    @Consumes(MediaType.APPLICATION_XML)
    public void update(Customer customer) {
        entityManager.merge(customer);
    }

    @DELETE
    @Path("{id}")
    public void delete(@PathParam("id") long id) {
        Customer customer = read(id);
        if(null != customer) {
            entityManager.remove(customer);
        }
    }

    @GET
    @Produces(MediaType.APPLICATION_XML)
    @Path("findCustomersByCity/{city}")
    public List<Customer> findCustomersByCity(@PathParam("city") String city) {
        Query query = entityManager.createNamedQuery("findCustomersByCity");
        query.setParameter("city", city);
        return query.getResultList();
    }

}

If you want to use the same domain objects on the server and client side. Then I would provide the JPA mappings via XML rather than annotations to avoid a classpath depedency on the client.

For More Information

- Part 1 - Data Model

- Part 2 - JPA

- Part 3 - JAXB (using MOXy)

- Part 4 - RESTful Service (using an EJB session bean)

- Part 5 - The client

UPDATE

META-INF/persistence.xml

The persistence.xml file is where you specify a link to the XML file that contains the JPA mappings:

<persistence-unit name="CustomerService" transaction-type="JTA">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <jta-data-source>CustomerService</jta-data-source>
    <mapping-file>META-INF/orm.xml</mapping-file>
</persistence-unit>

META-INF/orm.xml

It is in this file that you would add the XML representation of the JPA metadata.

<?xml version="1.0" encoding="UTF-8"?>
<entity-mappings
    version="2.0"
    xmlns="http://java.sun.com/xml/ns/persistence/orm"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm http://java.sun.com/xml/ns/persistence/orm_2_0.xsd">
    <entity class="org.example.Customer">
         <named-query name="findCustomersByCity">
            <query>SELECT c FROM Customer c WHERE c.address.city = :city</query>
         </named-query>
         <attributes>
            <id name="id"/>
            <basic name="firstName">
                <column name="FIRST_NAME"/>
            </basic>
            <basic name="lastName">
                <column name="LAST_NAME"/>
            </basic>
            <one-to-many name="phoneNumbers" mapped-by="customer">
                <cascade>
                    <cascade-all/>
                </cascade>
            </one-to-many>
            <one-to-one name="address" mapped-by="customer">
                <cascade>
                    <cascade-all/>
                </cascade>
            </one-to-one>
         </attributes>
    </entity>
    <entity class="org.example.Address">
        <attributes>
            <id name="id"/>
            <one-to-one name="customer">
                <primary-key-join-column/>
            </one-to-one>
        </attributes>
    </entity>
    <entity class="org.example.PhoneNumber">
        <table name="PHONE_NUMBER"/>
        <attributes>
            <id name="id"/>
            <many-to-one name="customer">
                <join-column name="ID_CUSTOMER"/>
            </many-to-one>
        </attributes>
    </entity>
</entity-mappings>

For More Information

- Creating a RESTful Web Service - Part 2/5 (XML Metadata)

Problem

Original source